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AD8644AR-REEL7 Scheda tecnica(PDF) 11 Page - Analog Devices |
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AD8644AR-REEL7 Scheda tecnica(HTML) 11 Page - Analog Devices |
11 / 16 page AD8614/AD8644 Rev. B | Page 11 of 16 CAPACITIVE LOAD DRIVE The AD8614/AD8644 exhibit excellent capacitive load driving capabilities. Although the device is stable with large capacitive loads, there is a decrease in amplifier bandwidth as the capacitive load increases. When driving heavy capacitive loads directly from the AD8614/AD8644 output, a snubber network can be used to improve the transient response. This network consists of a series R-C connected from the amplifier’s output to ground, placing it in parallel with the capacitive load. The configuration is shown in Figure 28. Although this network does not increase the bandwidth of the amplifier, it does significantly reduce the amount of overshoot. AD86x4 VOUT 5V RX CX CL VIN Figure 28. Snubber Network Compensation for Capacitive Loads The optimum values for the snubber network should be determined empirically based on the size of the capacitive load. Table 4 shows a few sample snubber network values for a given load capacitance. Table 4. Snubber Networks for Large Capacitive Loads Load Capacitance (CL) Snubber Network (RX, CX) 0.47 nF 300 Ω, 0.1 μF 4.7 nF 30 Ω, 1 μF 47 nF 5 Ω, 10 μF DIRECT ACCESS ARRANGEMENT Figure 29 shows a schematic for a 5 V single-supply transmit/ receive telephone line interface for 600 Ω transmission systems. It allows full duplex transmission of signals on a transformer- coupled 600 Ω line. Amplifier A1 provides gain that can be adjusted to meet the modem’s output drive requirements. Both A1 and A2 are configured to apply the largest possible differential signal to the transformer. The largest signal available on a single 5 V supply is approximately 4.0 V p-p into a 600 Ω transmission system. Amplifier A3 is configured as a difference amplifier to extract the receive information from the transmission line for amplification by A4. A3 also prevents the transmit signal from interfering with the receive signal. The gain of A4 can be adjusted in the same manner as A1 to meet the modem input signal requirements. Standard resistor values permit the use of single in-line package (SIP) format resistor arrays. Couple this with the AD8644 14-lead SOIC or TSSOP package and this circuit can offer a compact solution. 6.2V 6.2V 2kΩ 1:1 1 2 3 7 6 5 2 3 1 6 5 7 5V DC A1, A2 = 1/2 AD8644 A3, A4 = 1/2 AD8644 R12 10kΩ R11 10kΩ R10 10kΩ R13 10kΩ R14 14.3kΩ C2 0.1µF RECEIVE RxA 2kΩ 10µF P2 Rx GAIN ADJUST R7 10kΩ R8 10kΩ R9 10kΩ R6 10kΩ R5 10kΩ TRANSMIT TxA C1 0.1µF R1 10kΩ R2 9.09kΩ P1 Tx GAIN ADJUST R3 360Ω TO TELEPHONE LINE ZO 600Ω T1 MIDCOM 671-8005 A1 A2 A3 A4 Figure 29. A Single-Supply Direct Access Arrangement for Modems A ONE-CHIP HEADPHONE/MICROPHONE PREAMPLIFIER SOLUTION Because of its high output current performance, the AD8644 makes an excellent amplifier for driving an audio output jack in a computer application. Figure 30 shows how the AD8644 can be interfaced with an ac codec to drive headphones or speakers. U1-A 4 5V 1 10 2 3 5 5V AVDD1 VREFOUT LINE_OUT_L LINE_OUT_R AVSS1 7 8 6 9 NOTES 1. ADDITIONAL PINS OMITTED FOR CLARITY. U1-B U1 = AD8644 28 35 36 26 25 + AD1881A (AC'97) R3 20Ω + C1 100µF R1 2kΩ R4 20Ω C2 100µF R2 2kΩ Figure 30. A PC-99-Compliant Headphone/Line Out Amplifier |
Codice articolo simile - AD8644AR-REEL7 |
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Descrizione simile - AD8644AR-REEL7 |
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